Will traumatic stress sharpen your memory ... or sabotage it?

What The Latest Findings Reveal

An East Coast officer was telling an interviewer about the night he was ambushed from a passing car and half his face was blown away by a shotgun. "One thing I'll never forget is that license plate," he declared. He confidently recited the number seared into his mind.

Turns out it was wrong. His memory of the most hellish instant of his life wasn't what he thought it was.

It's commonly believed that memories formed under stress are more accurate than those imprinted by ordinary circumstances. The logic is that as the level of personal threat or relevance increases, the more important the memory becomes and thus the more vividly it gets etched into your brain. The higher the stress, the more accurately you'll remember.

But now a new study of memories related to traumatic events challenges that common wisdom. When stress becomes intense enough, the study reveals, it significantly hampers accurate recall in many cases and indeed may even lead to the creation of totally false "recollections."

"This is consistent with a growing body of anecdotal evidence gathered from law enforcement officers [like the shotgun survivor] who've experienced shootings and other life-threatening encounters," says Dr. Bill Lewinski, executive director of the Force Science Research Center at Minnesota State University-Mankato. "It raises major doubts about the reliability of memories concerning extreme events involving officers and civilian victims alike."

The new study, groundbreaking in its realism, was conducted by a research team led by Dr. Charles Morgan III, an associate professor of psychiatry at Yale University's medical school, and tested some 500 military personnel at the rigorous U.S. Army Survival School. While undergoing evasion training in a wilderness area, participants were "captured" and confined in a mock prisoner-of-war camp, where they were deprived of food and sleep for 48 hours before being subjected to intense interrogations.

Each individual experienced both "low-stress" and "high-stress" questioning lasting about 40 minutes per session, with a four-hour break in between. Low-stress interviews involved an interrogator trying to trick the subject into divulging information, but the high-stress interrogations included "real physical confrontations" described as "manhandling." Measurements of heart rates, adrenalin, stress hormone levels and other physiological and biochemical indicators confirmed that all participants "did indeed experience high levels of traumatic stress."

While these circumstances obviously differ from the on-duty confrontations cops encounter, the stress load inflicted was "comparable to real-world, threat-to-life events," Morgan concluded. In other words, as Lewinski puts it, "the sheer terror of an officer coming face-to-face with his or her possible death" in a shooting, for example, would not likely be any less stressful than the experiment. Similar results could reasonably be anticipated.

Twenty-four hours after being released from the mock prison and after food and rest, the study participants were asked to make eyewitness identification of their interrogators. Some were asked to pick the "suspect/perpetrator" out of a live line-up, others were shown photographs spread in front of them and still others were presented with photos in sequential order--the common identification procedures used by law enforcement.

"The overall performance of participants was alarmingly inaccurate," says Dr. Jonathan Page, who has reviewed the study. Page is an assistant professor of neuropsychology at Minnesota State and a technical advisor to the Force Science Research Center.

Despite having spent 40 minutes face-to-face with their interrogators, only 30 per cent of the participants were able to accurately pick their high-stress "perpetrator" from a live line-up and only 34 per cent were able to do so from a photo spread. Performance was better--about half succeeded accurately--using what proved to be the best method for stimulating recall, the display of sequential photos.

Although a minority of testees did show better memory after high stress, most were far more accurate in recalling low-stress interrogators, whatever the method of prompting. Generally, the more severe the physical confrontation, the worse the participant was at recognizing the person who had interrogated him or her.

Indeed, some participants were not able to recall accurately even the gender of the person who interrogated them. And most not only failed to reliably recognize their interrogators but falsely and confidently identified people as their interrogators whom they had never even met.

"This is noteworthy," observes Page, "since military selection programs screen for individuals with superior skills of retention during life-threatening situations." In other words, these dismal memory results may actually be superior to those that would be expected from the general population.

Some earlier studies tended to support the popular "more stress equals better memory" assumption, Page notes. But in those experiments, participants generally were "shown videotapes or live re-enactments of crime scenes and then tested. Laboratory results relating to memory and stress can potentially be misleading since a willing participant in a controlled setting may not experience the same type or degree of stress" as someone involved in a real, uncontrollable encounter.

In a real or realistic event, an innate human coping mechanism may cause a subject to "dissociate" himself emotionally from the experience and this may disrupt the process by which memory is normally "encoded" in the brain, Morgan speculates.

Bottom line in his view: The study provides "robust evidence that eyewitness memory for persons encountered during events that are personally relevant, highly stressful and realistic in nature may be subject to substantial error."

While Morgan's findings have relevance to the reliability of information investigators may glean from traumatized crime victims, his study potentially has important implications also for surviving officers attempting to accurately recall details of a life-threatening encounter. "This study is valuable because it drives another nail in the coffin of the dangerous notion that people who experience trauma will retain a full memory of the event," explains Lewinski.

Technically, this study dealt only with the narrow ability to remember faces, and much remains to be researched and documented regarding the broader impact of stress on memory, Lewinski points out. Presently the FSRC is surveying existing studies in this area with the goal of designing new experiments that will specifically address an array of issues important to law enforcement. Because of their extensive experience in interviewing officers, a number of FSRC's national advisory board members will bring a vital foundation of expertise to this work, Lewinski says, including psychologists Alexis Artwohl and Kevin Gilmartin, firearms specialists Tom Aveni and Craig Stapp and others.

Meanwhile, Lewinski offers these suggestions to officers who may be trying to accurately recall details of traumatic events, as well as others who may be responsible for questioning such officers in an effort to learn what happened:

1. Be aware that memory of these events is far from foolproof. "Fighting for his life, an officer may be so focused on his survival that much of what happens will never register with him," says Lewinski. "Details simply will not be there to be recalled later. They didn't stick because they weren't important for him to pay attention to at the time. If he says he can't remember or if he 'remembers' something incorrectly, it doesn't necessarily mean he is lying or being uncooperative."

2. Don't try to fill in gaps in your memory by plugging in what seems logical. "There's a strong temptation to do this," Lewinski explains, "because the mind seeks the peace and sense of control that comes from reconstructing and understanding an event from start to finish. But that is simply not how memory retains information. Gaps are normal and inevitable. Better to live with them than to impose inventions that seem rational but may in fact come back to haunt you later."

3. After evidence and evidence markers have been removed, return to the scene of your traumatic event for an unpressured, unrecorded walk-through on your own. "This tends to stimulate and correct memory," says Lewinski. Force Science News subscriber Tom Totland, a deputy with Park County (MT) Sheriff's Office, for example, recalls that after surviving a shooting he "remembered" that he was about 15 yards away from the suspect when he fired two defensive rounds. When he returned to the scene, however, he realized he was actually "only 9 feet away when I pulled the trigger." As it turned out, that more accurate recollection helped an investigator make better sense of Totland's account of the incident.

4. An investigator's skill and style in questioning an involved officer can make a huge difference in what an officer remembers. The most reliable approach, Lewinski believes, is to use a "cognitive behavioral" interviewing technique which, in simplest terms, involves engaging all an officer's senses--hearing, sight, touch, taste, smell--in fully prospecting his memory bank. This technique takes special training to do properly, however.

Information on such training can be obtained from Dr. Ronald Fisher, a psychologist at Florida International University [phone 305-919-5853 or e-mail: fisherr@fiu.edu]. Fisher is co-author of the book, "Memory-Enhancing Techniques for Investigative Interviewing: The Cognitive Interview", published by the Charles C. Thomas company of Springfield, Ill.

Note: A full account of the study described in this report appears in the International Journal of Law and Psychiatry, vol. 27 (2004), pages 265-279, under the title "Accuracy of Eyewitness Memory for Persons Encountered During Exposure to Highly Intense Stress." A synopsis of this study, written in layman's language by FSRC's Jonathan Page especially for readers of Force Science News, appears on the Center's website: http://www.forcescience.com/visuals/stressmemory/

About the author

The Force Science Institute was launched in 2004 by Executive Director Bill Lewinski, PhD. - a specialist in police psychology -- to conduct unique lethal-force experiments. The non-profit Force Science Institute, based at Minnesota State University-Mankato, uses sophisticated time-and-motion measurements to document-for the first time-critical hidden truths about the physical and mental dynamics of life-threatening events, particularly officer-involved shootings. Its startling findings profoundly impact on officer training and safety and on the public's naive perceptions.
For more information, visit www.forcescience.org or e-mail info@forcescience.org. If you would benefit from receiving updates on the FSRC's findings as well as a variety of other use-of-force related articles, please visit www.forcesciencenews.com and click on the "Please sign up for our newsletter" link at the front of the site. Subscriptions are free.